11 Tips for Fiberglass Repair

Although it is an extremely strong material used for a variety of purposes including the body work for the famous Corvette sports car, fiberglass repair is needed when it has developed cracks or holes. When working with fiberglass you will want a seamless repair that will match the original. In order to do so, you will need to repair the hole from the inside out.

Before beginning your fiberglass repair project, you will need to have certain supplies available. They are listed below:

• tape

• grinder

• razor

• gelcoat

• resin roller

• fiberglass mat

• fiberglass fabric

• polyester resin  

• methyl ethyl ketone peroxide

• dewaxing solvent  

Once you have your supplies, you will be ready to repair the damaged fiberglass using the basic tips below:

1. Determine the Damage

If the damaged piece of fiberglass is not clearly visible, find it by tapping the fiberglass with a tool. If it is damaged, it will have a dull sound. Normal fiberglass sounds tight.

2. Work from the Inside

You will want to have a seamless repair on the outside. To accomplish this you will need to start the repair by working from the inside.

3. Taper the Damageed Area

Once you have located the damaged area, use a grinder to taper the hole. Tapering is necessary to provide the new laminate more surface on which to bond. As a result, the chances that the repair will work are increased.

4. Treat the Exterior Border

Use a de-waxing solvent to treat the exterior border of the hole. This helps to create a strong bond when the new fiberglass is applied.

5. Coat the Area

Use paste wax to coat the area around the hole to ensure that any resin that may run will not bond to the exterior that has not been damaged.

6. Prepare for Patching

For the bottom of the hole, you will need to screw or tape a waxed backer. This will provide a hard surface to work on when patiching the hole.

7. Match the Colors

Coat the waxed backer in a gelcoat to start the repair. You will need to match the colors because Gelcoat is a pigmented resin. This will create a smooth exterior finish that matches the undamaged fiberglass.

8. Layer the Mat and Fabric

You will need to cut the fiberglass fabric and the mat to match the size of the hole. Next, place in two layers of mat, then fabric and alternate the layers of fiberglass mat and fabric. However, any more than four layers will weaken your bond. The amount of mat and fabric that you use should be determined by the thickness of the fiberglass. 

9. Patch and Secure

To patch the hole and secure the fabric and mat, you can use polyester resin or epoxy. If you use polyester resin, you will also need a laminating resin to increase the bond's strength.

10. Harden the Resin

Use methyl ethyl ketone peroxide as a catalyst for hardening polyester resins. It is important to follow the manufacturer's directions to be sure you are using the correct amount. To remove air bubbles or bumps, use a resin roller.

11. Fill-in, Sand and Polish

 Use more gelcoat to remove the wax backer and to fill in any exterior imperfections. Afterwards, you may sand and polish as needed.

For larger projects specific to restoring fiberglass auto parts, and for step by step instructions with photos, check out more on Fiberglass Repair.